Vehicle equipment means devices adapted to take measurements or perform maintenance operations on vehicles or parts of ground vehicles, for example, wheel alignment, vehicle inspection, tyre removal, wheel balancing or engine diagnostic devices, lifts or a combination of these.
Contactless 3D structured light scanning systems are known in the vehicle equipment sector.
Such scanning systems, known for example in U.S. 2013271574, comprise a projector provided to project structured light onto a measurement object with a pattern, for example bright dots, one or more video cameras provided to arrange the pattern projected onto the measurement object, and a processing unit for the image acquired by the video cameras for the 3D reconstruction of the measurement object.
Such scanning systems are used for the 3D reconstruction of parts of vehicles, for example the wheels or parts of the bodywork, or mobile parts of other vehicle equipment, for example tyre removal arms or lifts, or parts of the operator's body, in order to recognise their controls.
3D scanning is performed by the processing unit by comparing the images with one another, acquired by the cameras, of the measurement object onto which the structured light is projected and potentially also comparing with said images the geometry of the pattern loaded a priori into the memory of the processing unit. In devices with only one camera, said comparison with the geometry of the pattern is necessary; in devices with more than one camera it is optional.
The projector preferably uses a laser source because, with respect to other sources such as LED or incandescent lamps, it is coherent and therefore allows diffractive optical elements (DOEs) to be exploited in order to create the pattern cheaply and efficiently, it has a narrow emission band and therefore allows narrow-band filters to be used for the video cameras improving the ambient light rejection, has a small emission area and therefore allows the optical power to be concentrated into small dots hence enabling the resolution of the pattern and therefore the 3D reconstruction to be increased.
The laser source normally consists of a lateral emission diode, which however objectively has a series of drawbacks.
In the first place, it has a high ratio between cost and ambient disturbance rejection. In fact, the rejection of ambient disturbances increases if the optical power increases and is distributed uniformly, but the cost increases with the optical power and with the same cost for increasing optical power the quality of the beam decreases and hence the uniformity of the optical power distribution. For this reason, in the vehicle equipment sector lateral emission diodes with limited optical power are currently used.
Secondly, it has a low maximum operating temperature and high sensitivity of the wavelength to temperature, making it necessary to connect the diode to a complex and costly thermoelectric cooler (TEC).
Thirdly, if it is used in combination with DOEs, it requires a complex and costly projection system for reducing the non-diffracted laser beam (zero order), potentially retro-activated, in order to verify correct operation, so as to fulfil safety requirements (see for example EP2475956).
Fourthly, it has reduced reliability for catastrophic failure, particularly in case of dust.